The navigation goes through +files/<filename> where file reference is
provided by context getFileByName(filename).

The requested file is proxied via LibraryFileAliasView,
making it possible to serve both public and restricted files.

This navigation approach only supports domains with unique filenames,
which is the case of IArchive and IBuild. It will probably have to be
extended in order to allow traversing to multiple files potentially
with the same filename (product files or bug attachments).